In some arc welding systems, the welding machines require some means of non-contact arc initiation. For example, welding power supplies may include a high frequency ignition circuit or a capacitor discharge circuit to assist in bridging the gap from the electrode to the workpiece. Still other power supplies may be configured to use a “touch start” in which the electrode is initially shorted to the workpiece, but then lifted to initiate an arc after the current from the power supply reaches a preset value, e.g., 20 A. When welding in AC mode, arc stability is an issue because there is a possibility the arc may not re-light each time the waveform goes through zero current when the polarity is switched. The typical arc voltage is usually less than 30 volts OCV. Thus, at reverse polarity, there is only about 50 volts OCV plus any voltage from the output choke to reestablish the arc. This voltage, however, may not always be enough to reestablish the arc, especially in welding power supplies that use SCRs (silicon controlled rectifiers) to control the output welding waveform. This is because SCRs are relatively slow in switching states and the waveform may not go through zero fast enough to maintain the arc. Accordingly, to ensure a stable arc, many welding power supplies also turn on the arc starters each time the polarity is switched.
For example, high frequency ignition circuits can be turned on each time the AC waveform changes polarity. The high frequency ignition circuit induces high voltage, high frequency pulses that generate sparks between the electrode and workpiece to initiate the arc. The high frequency ignition circuit is a reliable method of re-igniting the arc. However, the electrical noise from these high frequency ignition circuits can damage the electronics in modern welding power supplies and other sensitive equipment located in the vicinity or workplace. Accordingly, the industry is making every effort to reduce or eliminate the use of these high frequency ignition circuits. For example, modern welding power supplies (e.g., inverter/chopper based power supplies) typically use a superposition or a center tapped choke to reestablish the arc when the polarity is switched. Because these methods do not use high voltage, high frequency pulses, the sensitive electronics are less susceptible to getting damaged by the electrical noise. However, in extreme conditions, the welding process may still experience a “pop out,” i.e., the arc does not re-ignite. Further, once the energy in the choke circuit is released, the process will need to wait until it charges again. Additional information concerning superposition circuits and center-tap choke circuits can be found in U.S. Pat. No. 7,385,159, which is incorporated by reference herein in its entirety as background material.
In addition to the above problems, related art high frequency ignition circuits are not “smart” circuits in that they may operate even when not needed and/or do not communicate with the welding power supply's control system to optimize arc ignition/re-ignition. This is because these circuits are “add on” circuits that are either hard coded or analog, and are not configured to work directly with the welding power supply's control system. The “add on” circuits typically only have a few settings. In one setting, the high frequency ignition circuit is turned on every time the welding waveform changes polarity without regard to whether the arc is on or off. In another setting, the high frequency ignition circuit is used only to initiate the arc but not to reestablish the arc during normal operation. Although some “add on” high frequency ignition circuits have a setting in which they only turn on when there is no arc, the determination of arc/no arc is made by the “add on” circuit without regard to the welding process, i.e., the initiation and/or duration of the high frequency pulses are not controlled by the power supply's control system.
Even in DC welding, such as for example in DC TIG welding, re-ignition of the arc may be required in certain scenarios such as after a short circuit or after the output voltage has been switched off due to a long arc condition. Accordingly, some of the problems with the ignition circuits discussed above with respect to AC welding are also applicable to DC welding.
Further limitations and disadvantages of conventional, traditional, and proposed approaches will become apparent to one of skill in the art, through comparison of such approaches with embodiments of the present invention as set forth in the remainder of the present application with reference to the drawings.